This problem is a bit complex.
Giant Insurance companies do not have the capital to back up mot of the big claims, so to hedge their bets they take an insurance cover on their issued policies. This is very crucial in case of large high risk hi premium coverages like an Oil refinery, where the claims can run into hundreds of millions of dollars.
For example, assume an insurer sells 1000 policies, each with a $1 million policy limit. Theoretically, the insurer could lose $1 million on each policy – totaling up to $1 billion. It may be better to pass some risk to a reinsurer as this will reduce the ceding company's exposure to risk.
With the current sanction on banking channels any repayment from the Reinsurance companies would not be possible if it involves Iranian crude.
Also for people worried about how we will source our crude, remember that we are a net exporter of finished petroleum products. We import crude much beyond our own national needs. We have excess refinery capacity and that is the reason why Essar, Reliance were looking forward to export Petrol/Diesel to Pakistan which suffers from a serious refinery shortage.